Function and Acoustics of the Normal and Diseased Middle Ear

Statistical analysis of the human middle ear mechanical properties

Many experimental data on the human middle ear (ME) mechanics and dynamics can be found in the literature. Nevertheless, discussions about the uncertainties of these data are scarce. The present study compiles experimental data on the mechanical properties of the human ME. The summary statistics of mean and standard deviation of the data were collected and the coefficients of variation were computed and pooled. Moreover, the linear correlation and distribution were assessed for the ossicles' mass. Results show that, generally, the uncertainties of the stiffness properties of the tympanic membrane, ligaments, and tendons are larger than the uncertainties of the ossicles' mass. In addition, the uncertainties of the ME response vary across frequency. The vibration measures, such as the stapes' velocity normalized by the sound pressure at the tympanic membrane, are more uncertain than ME input impedance and reflectance. It is expected that the results presented in this study will provide the basis for the development of probabilistic models of the human ME.

Stochastic model of the human middle ear using a nonparametric probabilistic approach

Several mathematical models of the human middle ear dynamics have been studied since the mid-twentieth century. Despite different methods applied, all of these models are based on deterministic approaches. Experimental data have shown that the middle ear behaves as an uncertain system due to the variability among individuals. In this context, stochastic models are useful because they can represent a population of middle ears with its intrinsic uncertainties. In this work, a nonparametric probabilistic approach is used to model the human middle ear dynamics. The lumped-element method is adopted to develop deterministic baseline models, and three different optimization processes are proposed and applied to the adjustment of the stochastic models. Results show that the stochastic models proposed can reproduce the experimental data in terms of mean and coefficient of variation. In addition, this study shows the importance of properly defining the acceptable range of each input parameter in order to obtain a reliable stochastic model.

Comparative acoustic performance and mechanical properties of silk membranes for the repair of chronic tympanic membrane perforations

The acoustic and mechanical properties of silk membranes of different thicknesses were tested to determine their suitability as a repair material for tympanic membrane perforations. Membranes of different thickness (10-100μm) were tested to determine their frequency response and their resistance to pressure loads in a simulated ear canal model. Their mechanical rigidity to pressure loads was confirmed by tensile testing. These membranes were tested alongside animal cartilage, currently the strongest available myringoplasty graft as well as paper, which is commonly used for simpler procedures. Silk membranes showed resonant frequencies within the human hearing range and a higher vibrational amplitude than cartilage, suggesting that silk may offer good acoustic energy transfer characteristics. Silk membranes were also highly resistant to simulated pressure changes in the middle ear, suggesting they can resist retraction, a common cause of graft failure resulting from chronic negative pressures in the middle ear. Part of this strength can be explained by the substantially higher modulus of silk films compared with cartilage. This allows for the production of films that are much thinner than cartilage, with superior acoustic properties, but that still provide the same level of mechanical support as thicker cartilage. Together, these in vitro results suggest that silk membranes may provide good hearing outcomes while offering similar levels of mechanical support to the reconstructed middle ear.